The spinal clamping device of the prior art is generally composed of a pair of hooked means intended for clamping a deformed vertebra under treatment, as exemplified by the HALIFAX.TM. interlaminar clamp system made by the AME Corp. of the United States. Such conventional spinal clamping device as described above is defective in design in that it often fails to fix and retrieve the deformed vertebra view of the fact that its hooked means are fastened by the nuts, which are vulnerable to becoming loosened by various movements of the clamped vertebra. The shortcoming of the spinal clamping device of the prior art described above was also pointed out by Ronald Moskovich in his article entitled "Altantoaxial Arthrodesis Using Interlaminar Clamps", which was published in SPINE, 17(3), 261(1992). For more details, please refer to FIG. 5 and the text thereof in Moskovich's article mentioned above.
In addition, the spinal clamping device of the prior art mentioned above can not be used as an auxiliary fixation device between the two vertebral locking rods.
With a view to overcoming the drawbacks of the afore-mentioned spinal clamping device of the prior art, this inventor has disclosed in the pending U.S. patent applications Ser. Nos. 08/004,612 (filing date: Jan. 14, 1993) now abandoned and 08/004,610 (filing date: Jan. 14, 1993 now U.S. Pat. No. 5,352,225 a two-layered spinal clamping system, in which the adjustment of the distance between the two hooked means is attained by means of the screws engageable with the threaded slots of a flat plate. In addition, this inventor has further disclosed in the pending U.S. patent application Ser. No. 08/004,609 (filing date: Jan. 14, 1993) now abandoned a spinal clamping system in which the distance between the two hooked means of the system is adjusted by making use of a plurality of bevel hooking slots of a hooking member capable of retaining reversibly. However, these improved spinal clamping systems disclosed in the above-mentioned U.S. patent application are limited in that the distance between the two hooked means can not be adjusted at will and that the systems are not as effective as expected in locking and retrieving a deformed vertebra.